The term "stent" is intended to indicate in general those devices intended for endoluminal application (for example, in a blood vessel), usually effected by means of catheterization, with subsequent deployment in place so as to achieve local support of the lumen. The primary purpose of this is to eliminate and avoid the restenosis of the treated area. It is moreover noted that it has already been proposed in the art to use substantially similar structures in order to achieve the deployment and anchorage in situ of vascular grafts; naturally, this possible extension of the field of application is also to be understood as being included within the scope of the invention.
For a general review of vascular stents, reference may usefully be made to the work "Textbook of Interventional Cardiology" edited by Eric J Topol, W. B. Saunders Company, 1994 and, in particular, to section IV of volume II, entitled "Coronary Stenting".
Many patent documents have addressed this issue as shown, for example, by U.S. Pat. No. 4,503,569; U.S. Pat. No. 4,768,507; U.S. Pat. No. 4,776,337; U.S. Pat. No. 4,800,882; U.S. Pat. No. 4,830,003; U.S. Pat. No. 4,856,516; U.S. Pat. No. 4,886,062; U.S. Pat. No. 4,907,336; and EP-A-0 201 466.
Notwithstanding the extensive research and experimentation, as documented at the patent level, only a relatively small number of operative solutions have, until now, found practical application. This is due to various factors, among which the following problems or requirements may be mentioned:
ensuring that, while moving towards the treatment site, the stent is capable of adapting with sufficient malleability to the path taken, even as regards less curved sections such as those which may exist, for example, in some peripheral vessels; all of this without detrimentally affecting the ability of the stent to provide an effective support action once positioned and deployed; PA1 avoiding, or at least limiting, the longitudinal shortening effect which occurs in many stents on deployment, PA1 achieving the maximum homogeneity and uniformity in the expansion movement, avoiding (when this is not a required effect) a situation in which this movement manifests itself to an extent and at times which vary in different areas or sections of the stent; PA1 providing the wall of the lumen which is being supported with a support surface that is as extensive as possible; PA1 avoiding the origination of complex shapes and/or possible stagnation sites susceptible, especially in blood vessels, of giving rise to negative phenomena such as coagulation, thrombosis, etc.; and PA1 reconciling the requirements described above with the modality and criteria of simple production, reliability and the introduction of currently available technology.
The present invention, having the characteristics referred to specifically in the following claims, has the object of resolving, at least in part, the problems outlined above. To this end, the solution according to the present invention is capable of being integrated with at least some of the solutions described in co-pending U.S. patent application Ser. Nos. 08/964,158; 08/987,365; 08/997,597; 09/004,376, each of which are hereby incorporated by reference, and in the Italian patent application No. TO96A000655 all of which are assigned to the same assignee of the present application.